Rame e società

Copper and Carbon

Copper’s contributions towards reducing greenhouse gas emissions

Increasing the cross section of wires and cables, overhead railway lines, and motor and transformer windings can significantly increase electrical energy efficiency. Incorporating one extra kilogram of copper can save between 100 and 7,500 kilograms of greenhouse gas emissions (CO2e). At the same time, the energy savings achieved will, in the vast majority of cases, lead to lower costs over the life cycle of the system.

Every conductor in an electrical system has a built-in resistivity. This means that part of the electrical energy it carries is dissipated as heat and lost as useful energy. Generating this wasted electrical energy produces carbon emissions and consequently contributes to global warming.

An important initial decision, in seeking to reduce these losses, is to use copper as the conductor.

Differences in resistivity mean that a copper conductor has only 61% of the losses of the same diameter in aluminium. Once the decision for copper has been made, energy losses can be reduced further by increasing the diameter of the conductor. While this cannot be increased endlessly, the environmental optimum for transformer and motor windings, electrical cables and traction overhead lines lies at a significantly higher conductor size than prescribed by current standards. In addition, increasing the diameter will, in the vast majority of cases, reduce the life cycle cost of the system.


Figure 1: The most economic cable diameter is, in many cases, 3 sizes up from current standards

This means that investing in additional copper conductor material makes sense from both an environmental and an economic point of view.

The following examples describe how increasing the copper conductor diameter can reduce carbon emissions:

A 15 kW induction motor can save 15,320 kg of carbon emissions over its lifetime

A 15 kW low voltage induction motor pumps water, drives an air compressor or operates a ventilation system. Upgrading the motor, from a standard 89.4% to a higher efficiency of 91.8%, requires an increase in the copper conductor content from 8.3 to 10.3 kg. Assuming that the motor has a lifetime of twenty years and an average loading of 50% over 6,000 hours per year, the eco-design tool calculates a lifetime emission reduction of 15,320 kg of CO2e, using the average EU electricity mix. This is a CO2e reduction of 7,660 kg/per kg of additional copper.

National electricity mixes influence this figure significantly. In France, where nuclear power is predominant, the emission reduction is 1,550 kg CO2e/kg copper, while in Poland, where electricity is generated mainly from coal-fired power plants, the emission reduction is 15,980 kg of CO2e/kg copper over the lifetime of the motor.

A 1.6 MVA transformer can save 1,023 kg of carbon emissions per kg of copper

A 1.6 MVA oil-cooled transformer is used to connect industrial plants to the high or medium voltage public grid. Upgrading the transformer from an AA’ to a CC’ class, or to an amorphous iron core, results in increases in copper content of 220, and 720, kg respectively. Assuming a lifetime of thirty years and an average loading of 50% over 8,760 hours per year, the eco-design tool calculates a lifetime emission reduction, at the EU electricity mix, of 1,023 kg CO2e/kg copper for the CC’ transformer and 550 kg of CO2e/kg copper for the amorphous core transformer.

Electric wires used in a small office building can decrease carbon emissions by 6,000 kg

When sized using common cable design software, the electric wires for selected circuits in a small office building (~1000 m2) contain 32.5 kg of copper. Upsizing these by one standard calibre increases copper usage to 52.2 kg and decreases carbon emissions, at the EU electricity mix, by 6,000 kg over the lifetime of the cables. This equals a reduction of 400 kg CO2e/kg of additional copper. When sized to the lowest life cycle system cost, diameters would be even larger and copper usage would increase to 114 kg. The reduction in carbon emissions, compared to the base case, would be 11,100 kg over the lifetime of the cables, or 137 kg CO2e/kg of additional copper.

 

Figure 2: Comparing the carbon footprints of different cable sizes in various types of buildings. The base case is the international standard. S+1 and S+2 are cables upsized by one and two standard calibres. ‘Economic’ means designed to the lowest life cycle cost. ‘Carbon’ means designed to the lowest carbon footprint.

The most economic case requires a significant increase in the diameter and results in a carbon footprint that is close to optimal.

The overhead lines of Dutch railways could save 93 kg carbon emissions per kg of copper

The Dutch railway system uses 1.5 kV DC for its traction. Upgrading the diameter of its overhead lines from 500 to 800 mm2 would result in an additional copper use of 2,670 kg/kilometre of track. This upgrade would reduce the losses in the overhead lines, calculated with the average daily train schedule of the Dutch railways, by 488 MWh over the life-time of the system. The eco-design tool calculates, at the EU electricity mix, a lifetime carbon emission reduction of 93 kg of CO2e/kg of additional copper.

Multi-fold environmental pay-back

As these examples demonstrate, carbon emission savings are the highest for devices with a high utilisation rate and in countries with a high share of fossil fuels in the electricity generation mix. However, even in systems where lifetime demands are less severe, savings are still very substantial.

On the production side, approximately 3 kg of CO2e are emitted during the mining and production of each kg of copper [1]. This means the carbon emission savings of additional copper usage are to be divided by three to calculate the environmental payback factor.

In summary, lifetime carbon emission savings and the corresponding environmental payback factors for an additional kg of copper are as follows :

Application

CO2e emission reduction

Environmental payback factor

Traction overhead line

75 to 100 kg

25 to 33

Office building wire

100 to 400 kg

33 to 133

Transformers

500 kg

166

Electric motors

3,000 to 7,500 kg

1,000 to 2,500

Another very important environmental benefit of copper usage is its 100% recyclability, without any loss in performance, at the device’s end-of-life. While aluminium is also recyclable, performance limitations prevent it from being recycled into new conductors – it is standard practice to use primary aluminium.  

Another very important environmental benefit of copper usage is its 100% recyclability, without any loss in performance, at the device’s end-of-life. While aluminium is also recyclable, performance limitations prevent it from being recycled into new conductors – it is standard practice to use primary aluminium.  

Summary

Increasing the diameter of a copper conductor reduces harmful CO2e emissions. Associated benefits include high environmental payback factors, reductions in system life cycle costs and 100% end-of life recyclability.

References

[1] ECI, 2006, www.copper-life-cycle.org, providing up to date life cycle data on key products
[2] EPD, May 2000, Product Specific Requirements for Rotating Electrical Machines, available from www.environdec.com
[3] European Commission - DG TREN, 1999, Save: Technical, economical and cost-benefit analyses of energy efficiency improvements in industrial three-phase induction motors
[4] THERMIE, December 1999, THERMIE STR-1678-98-UK: the Scope for Energy Saving in the EU through the Use of Energy-Efficient Distribution Transformers, available from www.leonardo-energy.org
[5] Leonardo ENERGY, R. Targosz (ed) et al, February 2005, Global energy savings potential from high efficiency distribution transformers, available from www.leonardo-energy.org
[6] Frederik Groeman, July 2000, Optimal reduction of energy losses in catenary wires for DC railway systems, ref 98430138-TDP 00-12709, available from www.leonardo-energy.org
[7] Frederik Groeman, November 2001, Benefits of upgrading the overhead line of a DC railway line in the Netherlands – a simulation case study, available from www.leonardo-energy.org
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